Tangential drive module assembly and method of assembly for airflow induction

ABSTRACT

A fan module assembly includes at least one a rotatable fan ( 38 ) having blades ( 39 ) with tips of blades being joined by an annular fan band ( 42 ). An electrically conductive squirrel cage ( 46 ) is associated with the fan band to rotate therewith. Flux receiving structure ( 48 ) is associated with the fan band. A shroud ( 40 ) has a shaft ( 54 ) with the fan being associated with the shaft so as to rotate about the shaft and with respect to the shroud. Control structure ( 52 ) is mounted stationary with respect to the shroud generally adjacent to a portion of the fan band. The control structure is constructed and arranged to generate a changing magnetic field, generally at the radius of the fan band, which interacts with the flux receiving structure and the squirrel cage to cause the fan to be driven by tangential force.

This application claims the priority benefit of U.S. ProvisionalApplication No. 60/935,040, filed on Jul. 24, 2007 and the contentthereof is hereby incorporated by reference into this specification.

FIELD OF THE INVENTION

This invention relates to modules (electric motor, fan and shroudassembly) used in automotive, engine or battery cooling applications;however the same concept/method can be applied in other applicationssuch as HVAC (Heating Ventilation and Air Conditioning).

BACKGROUND OF THE INVENTION

A conventional engine cooling module is shown, generally indicated at10, in FIG. 1 and this type of module is described in the published U.S.Patent Application No. 20070024135, the contents of which is herebyincorporated by reference into this specification. The module includes ashroud 12, and a fan 14 and motor (not seen) for driving the fan 14. Themotor is enclosed inside the central shield 16 of the shroud 12. Thereare also dual modules 10′ as shown on FIG. 2 and these types of modulesinclude two motors 18, two fans 14, and one shroud 12′). However, inboth types of modules, the electric motor is a discrete subassembly andit is mounted on to the shroud at the center of the fan. A typicalelectric motor 18 used in these applications is shown in FIG. 3 (in thePatent Application No. 20070024135, shown in FIG. 6). The motor 18includes four subassemblies: first, the stator assembly (motor case 20with magnets 22 and ball bearing assembly 24); second, the armatureassembly (assembly of shaft 26, commutator 28 and armature core 30 withcopper windings (not shown)); and third, the brush card assembly 32; andfourth, the end cap assembly 34. These subassemblies are produced ondedicated assembly lines requiring a large capital investment. This isone of the disadvantages of the conventional brush type motor design.

In many new vehicle applications the shaft power (Pout) requirement ofthe engine cooling module is up to 800 W and considering thelife/durability requirements of OEM specifications the conventionalbrush type motor design is not suited for such applications. Typicallythe brush type motors are limited to a shaft power of 400 W.

To further explain the power limitation of the conventional brush typemotors the Shaft Power is defined by the following equation:P _(out) =T*S   (Eq. 1)

where the T=Torque [N*m] and S=Rotational Speed [radians/sec]; Thereforewith increasing shaft power requirement either the torque or the speed(or both) need to be increased proportionally.

However for optimum motor life the operating torque typically is limitedto 10 to 15% of stall torque. The fan speed also needs to be carefullyconsidered since fan noise is proportional to fan speed and the OEM'sspecifications require low noise levels even with increased powerrequirements. The change of fan noise in function of change of fan speedis graphically shown on FIG. 4. The graph function is defined by Eq. 2at equal power and fan air density and it was derived from commonlyknown fan laws shown on Eq. 3.L1−L2=8*log₁₀(S1/S2)   (Eq. 2)L1−L2=14*log₁₀(P1/P2)+8*log₁₀(S1/S2)+6*log₁₀(φ1/φ2)   (Eq. 3)

where L is noise (sound) power level measured

P is fan power

S is fan speed

φ is fan air density

Therefore an optimized high power module could be achieved if the motorcan operate at high torque and low speed and still meet adequate motorlife/durability with low sound levels.

Accordingly, there is a need to improve the engine cooling module designto reduce manufacturing cost, also can provide high power operations athigh torque and low operating speed and still meet life/durability andacoustics requirements.

SUMMARY OF THE INVENTION

An object of the invention is to fulfill the need referred to above. Inaccordance with the principles of an embodiment of the presentinvention, a fan module assembly includes at least one a rotatable fanhaving blades with tips of blades being joined by an annular fan band.An electrically conductive squirrel cage is associated with the fan bandto rotate therewith. Flux receiving structure is associated with the fanband. A shroud has a shaft with the fan being associated with the shaftso as to rotate about the shaft and with respect to the shroud. Controlstructure is mounted stationary with respect to the shroud generallyadjacent to a portion of the fan band. The control structure isconstructed and arranged to generate a changing magnetic field,generally at the radius of the fan band, which interacts with the fluxreceiving structure and the squirrel cage to cause the fan to be drivenby tangential force.

In accordance with another aspect of an embodiment of the invention, afan module assembly includes at least one a rotatable fan having bladeswith tips of blades being joined by an annular fan band. An electricallyconductive squirrel cage is associated with the fan band to rotatetherewith. Flux receiving structure is associated with the fan band. Ashroud has a shaft with the fan being associated with the shaft so as torotate about the shaft and with respect to the shroud. A stator assemblyis mounted stationary with respect to the shroud generally adjacent to aportion of the fan band. The stator assembly includes a stator core andstator windings associated with the stator core. The stator assembly isconstructed and arranged to generate a changing magnetic field,generally at the radius of the fan band, which interacts with the fluxreceiving structure and the squirrel cage to cause the fan to be drivenby tangential force.

In accordance with another aspect of an embodiment of the invention, amethod of driving a fan of a fan module of a vehicle provides at leastone a rotatable fan having blades with tips of blades being joined by anannular fan band, and an electrically conductive squirrel cage beingassociated with the fan band to rotate therewith. A flux receivingstructure is associated with the fan band. The method provides a statorassembly mounted stationary with respect to a shroud and generallyadjacent to a portion of the fan band. The stator assembly includes astator core and stator windings associated with the stator core. Thestator windings are energized thereby generating a changing magneticfield, generally at the radius of the fan band, which interacts with theflux receiving structure and the squirrel cage to cause the fan to bedriven by tangential force.

Other objects, features and characteristics of the present invention, aswell as the methods of operation and the functions of the relatedelements of the structure, the combination of parts and economics ofmanufacture will become more apparent upon consideration of thefollowing detailed description and appended claims with reference to theaccompanying drawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following detaileddescription of the preferred embodiments thereof, taken in conjunctionwith the accompanying drawings, wherein like reference numerals refer tolike parts, in which:

FIG. 1 is a view of a conventional “single” engine cooling module for avehicle.

FIG. 2 is a view of a conventional “dual” engine cooling module for avehicle.

FIG. 3 is an exploded view of a conventional motor used in the enginecooling modules of FIGS. 1 and 2.

FIG. 4 shows the graph of fan noise level change in function of changein fan speed (for constant fan power and air density)

FIG. 5 is a front view of a Tangential Drive Module (TDM) of anembodiment of the invention.

FIG. 6 is a rear view of the TDM of FIG. 5.

FIG. 7 is a view of the components of the TDM of FIG. 5.

FIG. 8 is a view of a back iron ring of the TDM of FIG. 7.

FIG. 9 shows a section of back iron which can be used in place of thering of FIG.8.

FIG. 10 is a sectional view of another embodiment of the TDM assemblywith the section of back iron fixedly mounted onto the shroud.

FIG. 11 is a view of a one-piece stator core and back iron defining aG-core.

FIG. 12 is a view of an assembly of the G-core of FIG. 11 with a fan.

FIG. 13 is a view of a squirrel cage of the TDM.

FIG. 14 is view of a portion of the squirrel cage of FIG. 13 showing anangle β.

FIG. 15 shows the control structure of the TDM of FIG. 7.

FIG. 16 shows the stator core with coils of the control structure ofFIG. 15.

FIG. 17 is a stator core insulator for the control structure of FIG. 15.

FIG. 18 is a dual pole piece for a dual fan drive application of a TDM.

FIG. 19 is an embodiment of a dual TDM.

FIG. 20 is a sectional view of a portion of a TDM showing details of theassembly of a fan to a shroud.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

A fan module, herein called TDM (Tangential Drive Module), in accordancewith an embodiment of the invention, is shown generally indicated at 36in FIG. 5 (front view) and FIG. 7 (rear view). The TDM 36 uses similarcomponents (fan 38 with fan hub 58 and shroud 40) as the module 10 shownin FIG. 1. The TDM 36 fundamentally operates on similar electromagneticprincipals as the module 10 of FIG. 1, except the required torque isgenerated at larger radial distance (R2) than R1 (FIG. 1) in theconventional module 10. Also, the TDM 36 is a brushless system. R1,shown in FIG. 1, is the radial distance to the air gap of the motorwhere the flux is generated and R2 shown in FIG. 5 is the radius to thefan band 42.

In the TDM 36, the Torque is generated at the tip of the fan band 42 atradial distance of R2 and R2=n*R1; where n>1 and it is a rationalnumber. The value of R2 here is expressed as a function of R1 and “n”for the sake of comparison of the new TDM 36 to the conventional module10; however R2 is the fan radius and it can be any size.

The equation 4 below defines the Torque in [N*m], where F=tangentialforce [N] and R=radial distance to the applied force F and this measuredin [m].T=F*R   (Eq. 4)

To prove mathematically the advantage of the new module TDM 36 over theconventional module 10 of FIG. 1, the new torque value (T2) of the TDM36 can be calculated the following way:T1=F1*R1T2=F2*R2

However R2=n*R1 as defined above and assuming F2=F1

Therefore T2=n*T1, and by using Eq. 1 one can see that the shaft powercan be increased by n times at the same fan speed. Also higher shaftpower with lower or same sound levels can be achieved by proportionallyadjusting the speed and torque.

The desired speed and torque can be achieved by careful design of themagnetic poles of the stator (flux density) and the supply ordriving/switching frequency.

The three major sub-components/assemblies of TDM 36 are shown in FIG. 7.The fan 38 includes fan hub 58, blades 39, an electrically conductivesquirrel cage 46, and flux receiving structure in the form of a backiron 48, preferably molded into the annular fan band 42. The squirrelcage 46 can be insert molded, snap fit, pressed on riveted, etc., withrespect to the fan band 42 or fan lip 43. The fan lip 43 can beconsidered to be part of the fan band 42. FIG. 8 shows the back iron 48in the form of an annular ring. The back iron ring 48 can be molded orattached to the fan band 42 or to the fan lip 43 and thus rotates withthe fan 38. The back iron 48 in such applications is preferably made outof soft magnetic composite or lamination quality steel. FIG. 7 shows theshroud 40 and a control structure 52 with connector lead wire assembly61 for power input, generally indicated at 52. The control structure 52is a device that generates moving or changing magnetic field andcontrols rotational speed of the fan 38. The stator arms 44 of theshroud 40 support a shaft 54 that is received by bearing 88 (FIG. 20) ofthe fan 38.

An advantage of the TDM 36 is that the mass of the shroud 40 and statorarms 44 can be reduced because the arms 44 only support the fan mass andthe control structure 52. Lower supported mass at the center of theshroud can translate into higher first mode natural frequency underaxial excitation. (There is no heavy mass of the motor in the center ofthe shroud as in the conventional configuration of FIG. 1).

Alternatively, the back iron 48 can be just an arc-shaped section 50 ofa ring as shown in FIG. 9. In this case, the wall thickness of thesection is increased. FIG. 10 shows the section 50 mounted onto theshroud 40, generally adjacent to the control structure 52. The back ironsection 50 is made out of steel or soft magnetic composites. Thesquirrel cage 46 is insert-molded or mounted onto the fan band 42. Theorientation of the magnetic flux circuit and lines 55 are also shown inFIG. 10. The stator core 56 and windings 64 are disposed in the housing68 of the control structure 52.

The back iron also can be integral with the stator core 56. A “one piecestator core and back iron” (herein called G-core 56′) is shown in FIG.11. The G-core 56′ includes a first end 57 and an opposing second end59. The ends 57 and 59 are curved so as to receive a portion of the fanband 42 there-between (FIG. 12). The G-core 56′ can be manufactured from(but not limited to) a soft magnetic composite material and several ofthese G-cores would be mounted onto the shroud 40 together with thecontrol structure 52, depending on the magnetic flux requirement.

For clearer illustration purposes, FIG. 12 shows a simplified assemblyof the fan 38 and the G-core 56′. In FIG. 12, a typical fanconfiguration for an engine cooling application is shown with the newfeature of the insert molded squirrel cage 46 and the fan hub 58 withvent holes 60. The vent holes 60 are added into the hub 58 to minimizeradiator coverage. The magnetic flux circuits 62 are identified on theG-core 56′ together with the windings 64. An advantage of this structureover the two-piece part (shown in FIG. 10) is that the magnetic fluxcircuit has half of the number of air gaps. An air gap is identified ina magnetic flux circuit where the magnetic flux lines travel (jump)through other media or material than the steel/iron or some type ofmaterial such as air, plastic, wood and etc. . . . (these materials havesignificantly lower permeability than steel).

FIG. 13 shows the squirrel cage 46 preferably made out of a materialthat has good electrical conductivity, such as copper or aluminum. Thesquirrel cage 46 can be attached (molded or fastened) to the fan band 42or the lip 43 (FIG. 12).

The patterns on the squirrel cage are similar to the ones used ininduction motors. The angle β shown in FIG. 14 is typically skewed tominimize torque ripple and essentially reduce vibration and noise of thefan/module.

FIG. 15 shows the control structure 52 with lead wire and connector 61for electrical power input to 52 (cover and fastening features are notshown). The control structure 52 includes electronic structure 66 thatconveys power to the coils (stator windings 64) and provides logic andsequence to energize the coils. The electronic structure 66 can alsoprovide fault protection to the module such as over heat, overload, etc.Also the electronic structure 66 can be mounted outside of the 52somewhere else in the vehicle. The stator core 56 or 56′ is provided ina housing 68 of the control structure 52 and is associated with thestator windings 64. The housing 68 has a curved profile 70 that isconcentric with the fan band 42 or fan lip 43

The stator assembly, generally indicated at 71, including the statorcore 56 and stator windings 64 is shown in FIG. 16. The stator core 56is preferably made out of magnetic material steel laminations or moldedout of soft magnetic composites. The coils 64 can be wrappedindividually on each tooth 72 of the stator core 56 or over severalteeth. For a three phase-winding, the coil span would be over threeteeth and stator core 56 would have at least five teeth. The number ofturns of the stator winding or coils 64 depends on the applicationrequirement (for higher torque requirement the number of turns or theconductor size can be increased; also the stator core size can bechanged depending on the power requirement). Each stator tooth 72 has acurved profile 74 that is concentric with the fan band 42 of fan lip 43.

FIG. 17 shows a stator core insulator 76 the function of which is toelectrically insulate the coils 64 from the stator core 56. The teethprofiles 78 can be molded into the control structure 52 or into theshroud 40.

A dual pole core for a dual fan drive application of a TDM is shown,generally indicated at 80, in FIG. 18. The dual pole core 80 can beachieved with an H-core 82 and stator windings 64 as shown. The dualpole core 80 is part of the control structure 52 and can be provided ina housing (not shown). Terminals 81 and 83 are provided for the statorwindings 64. The H core can be placed into a protective housingsimilarly as 71 also fastened to the shroud at mounting holes 84. FIG.19 shows a dual TDM 36′ where two fans 38′ and 38″ are drivensimultaneously with the dual pole core there-between. The electronicstructure 66′ can be integrated into the module 36′ or can be placedsomewhere else in the vehicle.

One of the challenges of the TDM 36, 36′ is to maintain small air gapbetween the squirrel cage 46 and the stator core 56 and back iron 48 (orjust the G-core 56′) for optimum operation. Therefore it is important todevelop an assembly method that results in a tight assembly tolerance(low fan run out and tight positioning tolerance and concentricity offan and control structure 52 to shroud can results in low air gaprange). An example of fan attachment method is detailed on FIG. 20. OnFIG. 20 is shown a partial sectional view of a portion of the TDM 36detailing the assembly of the fan 38 to the shroud 40. The fan hub 58includes a bearing assembly, generally indicated at 86. The bearingassembly 86 includes at least one bearing 88 (two shown), a spacer 90and bearing retainers 92 retaining the bearings 88 and spacer 90 in thehub 58. The bearing assembly 86 permits the fan 38 to rotate about theshaft 54. The end of the shaft fixed to the shroud 40 can includeserrations or other surface features 94 to allow good bonding andengagement/locking of the shaft 54 to the shroud 40. An access hole 96is provided in the shroud 40 and is used to support the shaft 54 duringattachment. Also machining the surface of the fan band or lip aftermounted onto the shroud to reduce run out can be considered.

Some features of the embodiments are:

-   -   1. To drive at least one fan 38 tangentially by a changing        magnetic field (electromagnetic induction) at the radial        distance “R2” from the center of the fan; where “R2”        approximately equals to the radius of the fan band 42.    -   2. A squirrel cage 46 can be embedded into the fan band 42 or        the fan lip 43.    -   3. The operating torque can be increased by increasing number of        turns in the stator assembly or increasing the wire thickness or        the axial length of the unit.    -   4. To minimize radiator coverage/blockage and promote air flow        at ram air condition the fan hub size can be reduced. Also        openings can be added onto the fan hub for the same reason.    -   5. The squirrel cage 46 is preferably an integral part of the        fan band 42 and it rotates with the fan 38.    -   6. The control structure 52 that produces the changing magnetic        flux is stationary and it is mounted onto the shroud at a radial        distance of [(Fan radius)+(Fan run out)+(manufacturing        clearance)]    -   7. The back iron section 50 can also be stationary and can be        part of the control structure 52 mounted onto the shroud at a        radial distance of {[(Fan radius)−[(Fan run out)+(manufacturing        clearance)]}.    -   8. The back iron 48 and the squirrel cage 46 can be an integral        part of the fan band 42 or the fan lip 43.    -   9. The back iron 48 can be integrated into the stator core as        the G-core 56′.    -   10. Multiple fans 38′, 38″ can be driven at the same time.    -   11. One control structure 52 with H-core 82 can be placed        between two fans and same drive unit used to drive both fans        simultaneously at the same speed.    -   12. The control structure 52 can drive one or more fans at the        same time    -   13. More than one pole pieces can be placed together to form a        single part.    -   14. The control structure 52 provides protection to TDM.    -   15. The back iron 48 can be a section 50 of a ring.

The foregoing preferred embodiments have been shown and described forthe purposes of illustrating the structural and functional principles ofthe present invention, as well as illustrating the methods of employingthe preferred embodiments and are subject to change without departingfrom such principles. Therefore, this invention includes allmodifications encompassed within the spirit of the following claims.

1. A fan module assembly comprising: at least one rotatable fan havingblades, tips of blades being joined by an annular fan band, anelectrically conductive squirrel cage being associated with the fan bandto rotate therewith, flux receiving structure associated with the fanband, the flux receiving structure being made of soft magnetic materialthat can be magnetized but does not remain magnetized, a shroud having ashaft, the fan being associated with the shaft so as to rotate about theshaft and with respect to the shroud, and only one localized, singlecontrol structure mounted stationary with respect to the shroudgenerally adjacent to one portion of the fan band, the single controlstructure being constructed and arranged to generate a localized andbalanced changing magnetic field, generally at a radius of the fan band,which interacts with the flux receiving structure and the squirrel cageto alone cause the fan to be driven by tangential force without the useof permanent magnets.
 2. The fan module of claim 1, wherein the fluxreceiving structure is an annular flux ring coupled with the fan band.3. The fan module of claim 1, wherein the flux receiving structure is anarc-shaped section mounted stationary on the shroud, the fan band beingdisposed between the arc-shaped section and the control structure. 4.The fan module of claim 1, wherein the squirrel cage is embedded in thefan band.
 5. The fan module of claim 1, wherein the control structureincludes a stator core, stator windings associated with the stator coreand electronic structure constructed and arranged to convey power to thestator windings.
 6. The fan module of claim 5, wherein the stator corehas a portion with a curved profile that is concentric with respect tothe fan band.
 7. The fan module of claim 6, wherein the controlstructure further includes a housing, the stator core, the statorwindings, and the electronic structure being disposed in the housing,the housing having a curved profile receiving the curved profile portionof the stator core.
 8. The fan module of claim 6, wherein the portionwith a curved profile are stator teeth upon which the stator windingsare wound.
 9. The fan module of claim 7, further including a stator coreinsulator constructed and arranged to electrically insulate the statorwindings from the stator core.
 10. The fan module of claim 5, whereinthe flux receiving structure is integral with the stator core andincludes a first end and an opposing second end, the first end and thesecond end form a gap for receiving a portion of the fan bandthere-between, the second end is radially closer to an axis of rotationof the fan than the first end and the fan band includes an internalsurface and an external surface, wherein the internal surface isradially closer to the axis of rotation of the fan than the externalsurface, the ends being curved so as to receive the portion of the fanband there-between such that the first end is adjacent to the internalsurface and the second end is adjacent to the external surface.
 11. Thefan module of claim 1, wherein a first fan and a second fan areprovided, the first fan is rotatable about a first shaft of the shroudand the second fan is rotatable about a second shaft of the shroud, thefirst shaft and the second shaft are spaced from each other but parallelto each other, a flux receiving structure being associated with each fanband, and wherein the control structure includes a dual pole coredisposed between the fans and associated with the flux receivingstructures to drive the first fan and the second fan simultaneously. 12.A fan module assembly comprising: at least one rotatable fan havingblades, tips of blades being joined by an annular fan band, anelectrically conductive squirrel cage being associated with the fan bandto rotate therewith, flux receiving structure associated with the fanband, the flux receiving structure being made of soft magnetic materialthat can be magnetized but does not remain magnetized, a shroud having ashaft, the fan being associated with the shaft so as to rotate about theshaft and with respect to the shroud, and only one localized, singlestator assembly mounted stationary with respect to the shroud generallyadjacent to one portion of the fan band, the single stator assemblyincluding a stator core and stator windings associated with the statorcore, the single stator assembly being constructed and arranged togenerate a localized and balanced changing magnetic field, generally ata radius of the fan band, that interacts with the flux receivingstructure and the squirrel cage to alone cause the fan to be driven bytangential force without the use of permanent magnets.
 13. The fanmodule of claim 12, wherein the flux receiving structure is one of anannular flux ring coupled with the fan band or an arc-shaped sectionmounted stationary on the shroud with the fan band being disposedbetween the arc-shaped section and the stator assembly.
 14. The fanmodule of claim 12, further including electronic structure constructedand arranged to convey power to the stator windings.
 15. The fan moduleof claim 12, wherein the stator core has a portion with a curved profilethat is concentric with respect to the fan band.
 16. The fan module ofclaim 12, wherein the flux receiving structure is integral with thestator core and includes a first end and an opposing second end, thefirst end and the second end form a gap for receiving a portion of thefan band there-between, the second end is radially closer to an axis ofrotation of the fan than the first end and the fan band includes aninternal surface and an external surface, wherein the internal surfaceis radially closer to the axis of rotation of the fan than the externalsurface, the ends being curved so as to receive the portion of the fanband there-between such that the first end is adjacent to the internalsurface and the second end is adjacent to the external surface.
 17. Thefan module of claim 12, wherein a first fan and a second fan areprovided, the first fan is rotatable about a first shaft of the shroudand the second fan is rotatable about a second shaft of the shroud, thefirst shaft and the second shaft are spaced from each other but parallelto each other, a flux receiving structure being associated with each fanband, and wherein the stator core is a dual pole core disposed betweenthe fans and associated with the flux receiving structures to drive thefirst fan and second fan simultaneously.
 18. A method of driving a fanof a fan module of a vehicle, the method comprising: providing at leastone rotatable fan having blades with tips of blades being joined by anannular fan band, and an electrically conductive squirrel cage beingassociated with the fan band to rotate therewith, providing fluxreceiving structure associated with the fan band, the flux receivingstructure being made of soft magnetic material that can be magnetizedbut does not remain magnetized, providing only one localized, singlestator assembly mounted stationary with respect to a shroud andgenerally adjacent to one portion of the fan band, the single statorassembly including a stator core and stator windings associated with thestator core, and energizing the stator windings thereby generating alocalized and balanced changing magnetic field, generally at a radius ofthe fan band, which interacts with the flux receiving structure and thesquirrel cage to alone cause the fan to be driven by tangential forcewithout the use of permanent magnets.
 19. The method of claim 18,wherein the step of providing the flux receiving structure includesproviding one of an annular flux ring coupled with the fan band orproviding an arc-shaped section mounted stationary on the shroud withthe fan band being disposed between the arc-shaped section and thestator assembly.
 20. A fan module assembly comprising: at least onerotatable fan having blades, tips of blades being joined by an annularfan band, an electrically conductive squirrel cage being associated withthe fan band to rotate therewith, flux receiving structure associatedwith the fan band, a shroud having a shaft, the fan being associatedwith the shaft so as to rotate about the shaft and with respect to theshroud, and only one control structure mounted stationary with respectto the shroud generally adjacent to one portion of the fan band, thecontrol structure being constructed and arranged to generate a changingmagnetic field, generally at the radius of the fan band, which interactswith the flux receiving structure and the squirrel cage to cause the fanto be driven by tangential force, wherein the control structure includesa stator core, stator windings associated with the stator core andelectronic structure constructed and arranged to convey power to thestator windings, and wherein the flux receiving structure is integralwith the stator core and includes a first end and an opposing secondend, the first end and the second end form a gap for receiving a portionof the fan band there-between, the second end is radially closer to anaxis of rotation of the fan than the first end and the fan band includesan internal surface and an external surface, wherein the internalsurface is radially closer to the axis of rotation of the fan than theexternal surface, the ends receiving a portion of the fan bandthere-between such that the first end is adjacent to the internalsurface and the second end is adjacent to the external surface.